1. Field of the Invention
The present invention relates in general to turbine rotors and, in particular, to a turbine disk having a cooling air flowpath formed through an axially enlarged portion of the disk for radially pumping cooling air into a turbine blade.
2. Description of Prior Developments
Modern gas turbine engines use a portion of the compressor air to cool the turbine rotor blades and other engine components heated by the hot flowing exhaust gases. The turbine compressor must not only pump and pressurize the air that is supplied to the combustor, but the compressor must also pump the air needed for cooling the heated turbine components. There is a substantial amount of compressor energy invested in providing the required flow of turbine cooling air. Part of this energy is recovered when the cooling air eventually enters the turbine flowpath through small cooling holes formed through the turbine blades.
An example of a conventional turbine engine cooling air flow circuit is shown in FIG. 1. Compressor discharge air 10 passes through diffuser vanes 12 and into and around combustor 14. A portion of discharge air 10 is used to cool the stator nozzles 16, the blade shrouds 18 and the rotor blades 20.
The rotor blade cooling air 10(a) flows past combustor 14 and passes through holes 22 provided in an inducer vane support 24. The cooling air 10(a) then flows over inducer vanes 26 which accelerate the cooling air to rotor speed and turn the cooling air in the direction that the rotor is turning. The cooling air is then channeled to the radially outer portion of turbine rotor disk 33 through holes 44 formed through a forward rotating seal 36.
The cooling air 10(a) then flows through holes or slots 28 in a blade retainer flange 30 before entering the dovetail slots 32 which are located at the radially outer end of turbine disk 33. Cooling air 10(a) then flows into the rotor blades 20 via radially-extending internal cooling passages 29 formed through each rotor blade. The cooling air then exits from the rotor blade cooling passages 29 into the gas stream 34 in a known fashion. A single labyrinth seal 80 is positioned axially forwardly and radially inwardly of the forward rotating seal 36 for preventing most of the compressor discharge leakage air 11 from reaching the forward rotating seal 36.
As better seen in FIG. 2, the forward rotating seal 36 is equipped with a large diameter toothed labyrinth seal 38 which discourages the leakage of cooling air 10(a) into the gas stream 34. A two tooth labyrinth seal 40 that is attached to the forward seal 36 discourages compressor discharge leakage air 11 from leaking into the inducer air cavity 42. Because the labyrinth seals 38 and 40 are positioned radially outwardly at a relatively large distance from their center of rotation, they tend to move radially during engine operation and thus tend to leak a large amount of valuable cooling air 10(a) into the flowpath of gas stream 34. This leakage can be so significant that it reduces engine performance and increases fuel consumption.
Increased engine performance could be achieved if the cooling air 10(a) could be pumped from the holes 44 in the forward rotating seal 36 directly to the disk dovetail slots 32. Although such pumping could be accomplished by attaching fins or tubes on forward rotating seal 36 to circuit the cooling air 10(a) from the holes 44 to the dovetail slots 32, it would be difficult or impossible for the forward rotating seal to carry the additional load created by the additional tubes or fins, particularly at such a large radius. This approach is therefore considered impractical.
A large reduction in labyrinth seal leakage could, however, be achieved by reducing the diameters of these seals and thereby improve engine performance. Thus, a more direct and efficient way of increasing engine performance is to reduce the diameters of the labyrinth seals 38 and 40. Unfortunately, as seen in FIG. 3, when the labyrinth seal diameters are reduced, the air shield arm 50 correspondingly increases in length.
This increase in the length of air shield arm 50 is so great that the forward rotating seal 36 can no longer withstand the resulting increased centrifugal forces generated at the increased air shield arm diameters. In addition, the cooling air 10(a) must be pumped a considerable distance radially outwardly from the holes 44 in the rotating seal 36 to enter the dovetail slot 32 in the turbine disk 33.
If the air shield arm 50 cannot withstand the increased centrifugal forces of its own increased length, it certainly cannot withstand these forces plus the added centrifugal forces which would develop if air tubes or fins were added to it. Accordingly, a need exists for a forward rotating seal and rotor disk assembly which reduces the diameters of the labyrinth seals without increasing the diameter of the air shield arm 50 and which efficiently pumps the cooling air to the turbine disk dovetail slots 32.
An additional problem encountered with conventional forward rotating seal designs is associated with the presence of bolt holes 46 such as required in the design of FIG. 3. These holes are highly stressed due to the radial loads placed on them. The forward seal disk hub 52 is required to carry not only the labyrinth seals, but also some joint loads from disk flange 54 and from the rotor shaft flange 56.
The bolt holes 46 are thus located between two pull forces. The seal hub 52 is pulling radially inwardly while the radially outer portion of the rotating forward seal is pulling radially outwardly. The highly stressed bolt holes 46 can reduce the useful life of the forward seal. It would therefore be desirable to eliminate the bolt holes in the forward seal.
A similar stress problem is associated with the bolt holes 48 that are located between the rotor disk dovetail slots 32 in the rim of the turbine disk 33. These holes plus the bolt holes in the blade retainers 58 and 60 are stress risers which reduce the life of the blade disk and blade retainers. Thus, a further need exists for a forward seal and rotor disk assembly wherein the effect of any bolt holes is minimized or the bolt holes are eliminated.